Add a workaround for GCC constexpr bug

This turns the constexpr constructors into templates to silence errors when constexpr isn't valid.  We are also switching to 12.2 for GCC/cmake tests to prevent regressions (9.5 and 13.1 are already tested by GCC/bazel tests).

Fixes #12807

PiperOrigin-RevId: 532258101

.github/workflows/test_cpp.yml

@@ -235,7 +235,7 @@ jobs:
       - name: Run tests
         uses: protocolbuffers/protobuf-ci/docker@v1
         with:
-          image: us-docker.pkg.dev/protobuf-build/containers/test/linux/gcc:13.1-5.4.0-307caa02808127e49720f3e77d6a9f3b3ef5a915
+          image: us-docker.pkg.dev/protobuf-build/containers/test/linux/gcc:12.2-5.4.0-307caa02808127e49720f3e77d6a9f3b3ef5a915
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           entrypoint: bash
           command: >-